Bipolar electrode probe for ablation monitoring

ABSTRACT

An electromagnetic surgical ablation system having a generator adapted to selectively provide surgical ablative energy to an ablation probe, and methods of operating same, are disclosed. The system includes a controller operatively coupled to the generator, and at least one tissue sensor probe operatively coupled to the controller. The at least one tissue sensor provides a tissue impedance measurement to the controller. A sensor probe may be designated a threshold probe adapted to sense when tissue is sufficiently ablated, or, a critical structure probe adapted to protect an adjacent anatomical structure from undesired ablation. During an electromagnetic tissue ablation procedure, the controller monitors tissue impedance to determine tissue status, to activate an indicator associated therewith, and, additionally or alternatively, to activate and deactivate the generator accordingly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application, which claimspriority to, and the benefit of, U.S. patent application Ser. No.12/708,974, filed on Feb. 19, 2010, the disclosure of which is hereinincorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to systems and methods for providingenergy to biological tissue and, more particularly, to apparatus andmethods for sensing one or more properties of tissue at one or morelocations during a microwave ablation procedure.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types ofenergy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal,laser, etc.) are applied to tissue to achieve a desired result.Electrosurgery involves application of high radio frequency electricalcurrent to a surgical site to cut, ablate, coagulate or seal tissue. Inmonopolar electrosurgery, a source or active electrode delivers radiofrequency energy from the electrosurgical generator to the tissue and areturn electrode mines the current back to the generator. In monopolarelectrosurgery, the source electrode is typically part of the surgicalinstrument held by the surgeon and applied to the tissue to be treated.A patient return electrode is placed remotely from the active electrodeto carry the current back to the generator. In tissue ablationelectrosurgery, the radio frequency energy may be delivered to targetedtissue by an antenna or probe.

There are several types of microwave antenna assemblies in use, e.g.,monopole, dipole and helical, which may be used in tissue ablationapplications. In monopole and dipole antenna assemblies, microwaveenergy generally radiates perpendicularly away from the axis of theconductor. Monopole antenna assemblies typically include a single,elongated conductor. A typical dipole antenna assembly includes twoelongated conductors, which are linearly aligned and positionedend-to-end relative to one another with an electrical insulator placedtherebetween. Helical antenna assemblies include a helically-shapedconductor connected to a ground plane. Helical antenna assemblies canoperate in a number of modes including normal mode (broadside), in whichthe field radiated by the helix is maximum in a perpendicular plane tothe helix axis, and axial mode (end fire), in which maximum radiation isalong the helix axis. The tuning of a helical antenna assembly may bedetermined, at least in part, by the physical characteristics of thehelical antenna element, e.g., the helix diameter, the pitch or distancebetween coils of the helix, and the position of the helix in relation tothe probe assembly to which it is mounted.

The typical microwave antenna has a long, thin inner conductor thatextends along the longitudinal axis of the probe and is surrounded by adielectric material and is further surrounded by an outer conductoraround the dielectric material such that the outer conductor alsoextends along the axis of the probe. In another variation of the probethat provides for effective outward radiation of energy or heating, aportion or portions of the outer conductor can be selectively removed.This type of construction is typically referred to as a “leakywaveguide” or “leaky coaxial” antenna. Another variation on themicrowave probe involves having the tip formed in a uniform spiralpattern, such as a helix, to provide the necessary configuration foreffective radiation. This variation can be used to direct energy in aparticular direction, e.g., perpendicular to the axis, in a forwarddirection (i.e., towards the distal end of the antenna), or combinationsthereof.

Invasive procedures and devices have been developed in which a microwaveantenna probe may be either inserted directly into a point of treatmentvia a normal body orifice or percutaneously inserted. Such invasiveprocedures and devices potentially provide better temperature control ofthe tissue being treated. Because of the small difference between thetemperature required for denaturing malignant cells and the temperatureinjurious to healthy cells, a known heating pattern and predictabletemperature control is important so that heating is confined to thetissue to be treated. For instance, hyperthermia treatment at thethreshold temperature of about 41.5° C. generally has little effect onmost malignant growth of cells. However, at slightly elevatedtemperatures above the approximate range of 43° C. to 45° C., thermaldamage to most types of normal cells is routinely observed. Accordingly,great care must be taken not to exceed these temperatures in healthytissue.

In the case of tissue ablation, a high radio frequency electricalcurrent in the range of about 500 MHz to about 10 GHz is applied to atargeted tissue site to create an ablation volume, which may have aparticular size and shape. Ablation volume is correlated to antennadesign, antenna tuning, antenna impedance and tissue impedance. Tissueimpedance may change during an ablation procedure due to a number offactors, e.g., tissue denaturization or desiccation occurring from theabsorption of microwave energy by tissue. Changes in tissue impedancemay cause an impedance mismatch between the probe and tissue, which mayaffect delivery of microwave ablation energy to targeted tissue. Thetemperature and/or impedance of targeted tissue, and of non-targetedtissue and adjacent anatomical structures, may change at varying rateswhich may be greater, or less than, expected rates. A surgeon may needto perform an ablation procedure in an incremental fashion in order toavoid exposing targeted tissue and/or adjacent tissue to excessivetemperatures and/or denaturation. In certain circumstances, a surgeonmay need to rely on experience and/or published ablation probeparameters to determine an appropriate ablation protocol (e.g., ablationtime, ablation power level, and the like) for a particular patient.

SUMMARY

The present disclosure is directed to an electromagnetic surgicalablation system that includes one or more tissue sensor probes adaptedto sense a tissue property, e.g., tissue impedance, at or near anablation surgical site. Also disclosed is a controller module which mayinclude a sensor interface having one or more sensor inputs adapted toreceive a sensor signal from the one or more tissue sensor probes.Additionally or alternatively, one or more sensor interfaces may beprovided by the controller module. The disclosed sensor interface mayinclude an impedance measurement circuit that is adapted to perform aconversion of a raw signal, which may be received from the one or moretissue sensor probes, into an impedance measurement suitable forprocessing by a processor included within the controller.

The disclosed surgical ablation system may include a source of microwaveablation energy, such as a generator, that is responsive to a controlsignal generated by the control module. The one or more tissue sensorprobes, the controller, and the generator function cooperatively toenable a surgeon to monitor one or more tissue properties at, oradjacent to, an ablation surgical site. Additionally or alternatively,the described arrangement may enable the automatic control, activation,and/or deactivation of ablative energy applied to tissue to enableprecise control over the ablation size and/or volume created during anablation procedure.

In addition, the present disclosure provides an electromagnetic surgicalablation system having a generator adapted to selectively providesurgical ablative energy to an ablation probe. The ablation probe isoperably coupled to the generator and adapted to receive ablative energytherefrom, and to deliver said ablative energy to targeted tissue, e.g.,a tumor, polyp, or necrotic lesion. The disclosed system includes acontroller operatively coupled to the generator, the controllerincluding at least one processor, a memory operatively coupled to theprocessor, a sensor interface circuit operatively coupled to theprocessor and adapted to receive one or more impedance sensor signalsfrom one or more tissue sensor probes. Additionally or alternatively, atissue sensor probe may include additional sensor, such as withoutlimitation, a temperature sensor. In such an embodiment, the sensorinterface circuit may include a temperature sensor circuit operativelycoupled to the processor and adapted to receive a temperature sensorsignal from a tissue sensor probe.

In one aspect, a system in accordance with the present disclosure mayenable a surgeon to place one or more tissue sensor probes around atargeted ablation region, and/or between a targeted ablation region andan adjacent anatomical structure. During an ablation procedure, thecontroller may monitor the one or more sensors to track the progress ofthe ablation region as tissue is “cooked”, based at least in part uponan impedance change detected at the one or more probe locations. In anembodiment, a feedback signal may be provided to the surgeon, e.g., avisual, audible, and/or tactile indication, such that a surgeon mayfollow the ablation region formation in real-time or in near-real-time.Each probe may be positioned such that targeted tissue may be monitoredat various locations around, and/or distances from, an ablation probebeing utilized to deliver ablative energy to tissue.

A tissue sensor probe may be identified (e.g., assigned or tagged)and/or adapted as a “threshold” probe or a “critical structure” tag. Itis envisioned that a threshold tag may be configured to sense when thetissue associated therewith has reached an ablation threshold, e.g., thepoint at which the desired degree of desiccation has occurred. As tissueassociated with a given probe has reached the desired ablation state, anindicator associated with the sensor may be activated. When a pluralityof threshold probes are utilized, a surgeon may recognize when anablation procedure is completed by noting when all, or a sufficientnumber of, indicators associated with the various probes have beenactivated. In an embodiment, the controller may automatically deactivatea generator when all, or a sufficient number of, threshold probes havereached a predetermined threshold.

A probe identified as a “critical structure” probe may be configured toactivate an indicator, which may be an alarm indicator, when tissueassociated therewith is about to, but has not yet, received ablationenergy in excess of a predetermined safety threshold. Additionally oralternatively, the disclosed system may be configured to automaticallydeactivate an ablation generator when a predetermined number (e.g., oneor more) of indicators associated with a critical structure probe havebeen activated. While it is contemplated that a critical structure probemay be positioned between an operative field and an adjacent criticalanatomical structure, it should be understood that the presentdisclosure is in no way limited to such use and that the describedprobes and features may be advantageously utilized in any combinationfor any purpose.

Also disclosed is a method of operating an electromagnetic surgicalablation system. The disclosed method includes the steps of activatingan electrosurgical generator to deliver ablative energy to tissue andsensing a tissue impedance parameter from at least one tissue sensingprobe, which may be inserted into tissue. A determination is made as towhether a sensed tissue impedance parameter exceeds a predeterminedtissue impedance parameter threshold. In response to a determinationthat a sensed tissue impedance parameter exceeds a predetermined tissueimpedance parameter threshold, an action is performed, e.g., theelectrosurgical generator is deactivated and/or an indication ispresented.

The present disclosure also provides a computer-readable medium storinga set of programmable instructions configured for being executed by atleast one processor for performing a method of performing microwavetissue ablation in response to monitored tissue temperature and/ormonitored tissue dielectric properties in accordance with the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows a diagram of a microwave ablation system having anelectromagnetic surgical ablation probe and at least one tissue sensorprobe in accordance with the present disclosure;

FIG. 2 shows a block diagram of a microwave ablation system having anelectromagnetic surgical ablation probe and at least one tissue sensorprobe in accordance with the present disclosure;

FIG. 3 is a perspective view of a tissue sensor probe in accordance withthe present disclosure;

FIG. 4 is a side, cutaway view of a tissue sensor probe in accordancewith the present disclosure;

FIG. 5 is a flowchart showing a method of operation of a microwaveablation system having one or more tissue sensor probes in accordancewith the present disclosure; and

FIG. 6 illustrates a relationship between time, an impedance sensed by afirst tissue sensor probe, and an impedance sensed by a second tissuesensor probe in accordance with the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings; however, it isto be understood that the disclosed embodiments are merely exemplary ofthe disclosure, which may be embodied in various forms. Well-knownfunctions or constructions are not described in detail to avoidobscuring the present disclosure in unnecessary detail. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a basis for the claims and asa representative basis for teaching one skilled in the art to variouslyemploy the present disclosure in virtually any appropriately detailedstructure.

In the drawings and in the descriptions that follow, the term“proximal,” as is traditional, shall refer to the end of the instrumentthat is closer to the user, while the term “distal” shall refer to theend that is farther from the user.

FIG. 1 shows an embodiment of a microwave ablation system 10 inaccordance with the present disclosure. The microwave ablation system 10includes an electromagnetic surgical ablation probe 100 having a tapereddistal tip 120 and a feed point 122. The ablation probe 100 is operablyconnected by a cable 15 to connector 16, which further operably connectsprobe 100 to a generator assembly 20. Generator assembly 20 may be asource of ablative energy, e.g., microwave or RF energy in the range ofabout 915 MHz to about 10 GHz. The disclosed system 10 includes one ormore tissue sensor probes 200 that are adapted to sense one or moreoperative parameters, e.g., a tissue impedance. The tissue sensor probe200 is operably connected by a cable 14 to a connector 18, which furtheroperably connects tissue sensor probe 200 to a controller assembly 30.An actuator 40 is operably coupled to the controller to enable a user,e.g., a surgeon, to selectively activate and de-activate the delivery ofablative energy to patient tissue. Controller 30 is operably coupled togenerator 20 to enable communication therebetween, such as withoutlimitation, a control signal and/or a status signal.

In more detail, FIG. 2 illustrates a functional block diagram of anablation system 10 in accordance with the present disclosure. The system10 includes a controller 30 that includes one or more processors 31operatively coupled to memory 32, storage device 33, sensor interface34, and user interface 35. Processor 31 is configured to execute a setof programmed instructions for performing a method of microwave ablationas disclosed herein. Memory 32 and/or storage device 33 may include anysuitable memory device, including without limitation, semiconductormemory (e.g., random-access memory, read-only memory, flash memory),hard disk, optical storage (e.g., CD-ROM, DVD-RAM, etc.), USB memorystick, and the like.

Controller 30 includes an actuator interface 36 that is adapted tofacilitate operative coupling with actuator 40 and/or a generatorinterface 37 that is adapted to facilitate operative coupling withgenerator 20. Actuator 40 may be any suitable actuator, such as withoutlimitation, a footswitch, a handswitch (which may be mounted on a probe100 and/or a tissue sensor probe 200), an orally-activated switch (e.g.,a bite-activated switch and/or a breath-actuated switch), and the like.The processor 31, memory 32, storage device 33, sensor interface 34,actuator interface 36 and/or generator interface 37 may be separatecomponents or may be integrated, such as in one or more integratedcircuits. The various components in the controller 30 are coupled by oneor more communication buses or signal lines 38. Memory 30 and/or storagedevice 33 may include a set of executable instructions for performing amethod of microwave ablation as described herein. One or more elementsof ablation system 10 may be coupled using a hard-wired connection(e.g., copper wire and/or fiber optic media) and/or a wireless link.During use, the one or more tissue sensor probe 200 may be positioned intissue T in proximity to probe 100 to obtain one or more tissueparameter(s), e.g., tissue impedance.

User interface 35 may include any suitable form of visual, audible, ortactile user interface elements, including without limitation, a graphicdisplay panel (e.g., LCD, LED, OLED plasma, gas-discharge display, andthe like), touchscreen, keypad, pushbutton, switch, lamp, annunciator,speaker, haptic feedback device, and so forth.

As shown in FIG. 2, and by way of example only, an ablation probe 100 isinserted into tissue T for use. A tissue sensor probe 200 is insertedinto tissue T in a position generally adjacent to probe 200. Anothertissue sensor probe 200′ is inserted into tissue T at a position furtherfrom probe 100. Yet a third tissue sensor probe 200″ is inserted intotissue T at a position generally between probe 100 and a criticalanatomical structure CS. During use, ablative energy from probe 100 isdelivered into tissue T to effectuate ablation of at least a part oftissue T. Denaturation of tissue T proceeds generally outwardly fromfeed point 122. As the volume of denatured (ablated) tissue expands, animpedance boundary expands in a corresponding manner.

It has been observed that during an initial phase of an ablationprocedure, tissue impedance will remain relatively constant. As tissueapproaches denaturation (e.g., as tissue becomes “cooked”), impedancetends to rise rapidly. By sensing the impedance at one or more pointssurrounding the ablation probe 100, the formation of the ablated volumeof tissue may be accurately monitored. In turn, the delivery of ablativeenergy may be controlled in response to the one or more impedancemeasurements obtained from the surrounding tissue. Thus, a surgeon maydefine a desired ablation region by deliberately positioning one or moretissue sensor probes 200 at or near the outer boundaries of the desiredregion. As each probe 200 senses a rise in impedance (which may signifytissue denaturation has occurred), a corresponding indication may bepresented to a user (e.g., a surgeon) that ablation of the tissuecorresponding to the probe has completed. An indication may be presentedvia user interface 35. The defined ablation volume is deemed fullyablated once each designated tissue probe 200 has sensed an impedancerise corresponding to denaturation. An “ablation complete” indicationmay then be presented to the user, or, additionally or alternatively,the generator 20 may be automatically deactivated. In this manner, theablation region may be precisely controlled with greatly reduced risk ofover-ablation and/or excessive charring of tissue or injuring criticalstructures.

The tissue probe(s) 200 may be designated as a threshold probe or acritical structure probe. One or more threshold probes may be used todefine an ablation volume by deliberate placement in tissue by asurgeon, as described hereinabove. The one or more threshold probe(s)may be grouped to define a threshold group, whereby an ablation completestatus is established when each threshold probe in a group has sensed animpedance rise corresponding to tissue denaturation. In contrast, acritical structure probe may be used to recognize a pre-denaturationstate of tissue, such as without limitation, an initial slight orgradual rise in impedance which may precede a more pronounced or rapidrise in impedance associated with tissue denaturation. In an embodiment,if any one critical structure probe senses pre-denaturation, anindicator may be presented to the user and/or generator 200 deactivated.In this manner, undesired ablation of one or more critical anatomicalstructures at or near the ablation site may be prevented.

A graph illustrating a relationship between sensor position, ablationtime, and tissue impedance (shown generally as 400) is presented in FIG.6, wherein a first impedance curve 405 corresponding to a first tissuesensor probe 200, and a second impedance curve 410 corresponding to asecond tissue sensor probe 200′, are shown. Initially, as ablationenergy is first delivered to tissue, both tissue sensor probes 200 and200′ indicate a relatively constant impedance value 401. As ablationtime t progresses, tissue surrounding first tissue sensor probe 200begins to denature, as illustrated by a rise in impedance 406. Asablation continues, the volume of denatured tissue expands, andeventually, reaches second tissue sensor probe 200′, as illustrated by asecond rise in impedance 411. Denaturation may be indicated by, e.g., anabsolute rise in impedance, a change in impedance from an initialimpedance value, and/or rate of change of impedance exceeding apredetermined rate.

Designation of a tissue probe 200 as a threshold probe or a criticalstructure probe may be accomplished manually by, e.g., a user enteringthe appropriate designation via user interface 35. Additionally oralternatively, a tissue probe 200 may include an identifier (notexplicitly shown) that identifies to controller 30 the probe as athreshold probe, a critical structure probe, or a universal probe whichmay function as either a threshold probe or a critical structure probe.The identifier may include, without limitation, an RFID tag, asemiconductor memory device (e.g., ROM, EEPROM, NAND or NOR flashmemory), an encoded electrical component (encoded resistor value), amechanical identifier (e.g., physically encoded connector member), anoptical identifier (e.g., a barcode) and the like. In an embodiment, auser entry may override an identifier-defined designation of a probe200.

A tissue sensor probe 200 in accordance with an embodiment of thepresent disclosure is now described with reference to FIGS. 3 and 4. Thedisclosed tissue sensor probe 200 includes an elongated shaft 210 havinga proximal end 213 and a distal end 211. A tapered tip 220 may bedisposed at a distal end 211 of the probe 200 to facilitate theinsertion of probe 200 into tissue. As shown, tapered tip 220 has agenerally conical shape; however, any suitable tip shape may beutilized. A pair of electrodes 222, 224 are disposed on an exteriorportion of the shaft 210. As shown, electrodes 222, 224 aresubstantially annular in shape and disposed coaxially about the shaft210; however, other electrode arrangements are contemplated within thescope of the present invention, including without limitation,longitudinal electrodes, helical electrodes, dot-shapes electrodes, andso forth. Electrodes 222, 224 may be formed from any suitablebiocompatible and electrically conductive material, such as withoutlimitation, stainless steel. In an embodiment, electrodes 222, 224 aredisposed generally toward a distal end 211 of the shaft 210; however, itis to be understood that either or both electrodes 222, 224 may bepositioned at other locations along shaft 210.

The probe 200 includes a pair of conductors 226, 228 that are configuredto place electrodes 222, 224, respectively, in electrical communicationwith controller 30 via cable 14 and/or connector 18. A distal end ofconductor 226 is electrically coupled to electrode 222. A distal end ofconductor 228 is electrically coupled to electrode 224. The connectionbetween conductors 226, 228 to electrodes 222, 224, respectively, may beformed by any suitable manner of electrical or electromechanicalconnection, including without limitation soldering, brazing, welding,crimping, and/or threaded coupling. Cable 14 extends from a proximal end213 of shaft 210, and may be supported by a strain relief 214.

Shaft 210 and electrodes 222, 224 may be formed by any suitable mannerof manufacture. In an embodiment, shaft 210 may be formed by injectionovermolding. By way of example only, shaft 210 may be formed from a highstrength, electrically insulating material, e.g., fiber-reinforcedpolymer, fiberglass resin composite, long strand glass-filled nylon, andthe like. During use, probe 200 may be inserted into tissue, placingelectrodes 222, 244 into electrical communication with tissue therebyenabling sensor interface 34, and controller 30 generally, to obtain animpedance measurement thereof.

Turning to FIG. 5, a method 300 of operating an electromagnetic surgicalablation system having an ablation probe 100, and one or more tissuesensor probe(s) 200, is shown. The disclosed method begins in step 305wherein one or more initializations may be performed, e.g., power-onself test (POST), memory allocation, input/output (I/O) initialization,and the like. In step 310, each of the tissue sensor probes to be usedin the ablation procedure is designated as a threshold probe or acritical structure probe. In an embodiment, the user (e.g., a surgeon oran assisting practitioner) may manually input a correspondingdesignation for each tissue sensor probe. Additionally or alternatively,the tissue sensor probe may be automatically identified by an identifierincluded within the probe 200 and sensed by controller 30 and/or sensorinterface 34 as described hereinabove.

A threshold value for each tissue sensor probe 200 may be established.In one embodiment, a threshold value for a threshold tissue sensor maydiffer from a threshold value for a critical structure tissue sensor. Athreshold may be an absolute threshold, e.g., exceeding a fixedimpedance value; a relative threshold, e.g., exceeding a predeterminedchange in impedance; or a rate threshold, e.g., where the rate ofimpedance change exceeds a predetermined rate. Other thresholds arecontemplated within the scope of the present disclosure, includingwithout limitation, spectral-based thresholds, wavelet-based thresholds,and impedance contour recognition thresholds.

The total number of tissue sensor probes designated for use during anablation procedure may be represented as n. In step 315, the one or moretissue sensor probes are inserted into tissue in accordance withsurgical requirements. In particular, a threshold probe is placed at ornear an outer boundary of the desired ablation region, while a criticalstructure probe is positioned between the intended ablation region and acritical anatomical structure to be protected. In addition, an ablationprobe 100 is positioned or inserted into tissue, e.g., the ablationsite.

Once the ablation probe 100 and the one or more tissue sensor probes 200have been positioned, the generator 20 is activated in step 320 to causeelectromagnetic ablative energy to be delivered to tissue. Generally,activation of generator 20 will be effectuated in response to engagementof actuator 40. During the ablative energy delivery process, theimpedance of each designated tissue sensor probe is monitored. In step325 a monitoring loop is established wherein a tissue sensor probecounter x is initialized, e.g., set to address the first of thecurrently-utilized one or more tissue sensor probes 200, which may beexpressed as probe(x). In step 330, an impedance value of thecurrently-addressed tissue sensor probe 200, which may be expressed asZprobe(x), is compared to a corresponding threshold value. If Zprobe(x)does not exceed a corresponding threshold value, the method proceeds tostep 335 wherein it is determined whether the generator is to bedeactivated, e.g., the user has released actuator 40. If, in step 335,it is determined that the generator 20 is to be deactivated, in step 365the generator is deactivated and the process concludes with step 370.

If, in step 335 it is determined that the generator 20 is to remainactivated, in step 355 the tissue sensor probe counter x is incrementedto address the next tissue sensor probe in use and in step 360, thetissue sensor probe counter is compared to the total number of tissuesensor probes designated for use. If in step 360 it is determined thatthe tissue sensor probe counter exceeds the total number of tissuesensor probes designated for use, the tissue sensor probe counter x isre-initialized in step 325; otherwise, the method continues with step330 wherein the impedance value of a subsequent tissue sensor probe 200is evaluated.

If, in step 330, it is determined that Zprobe(x) exceeds a correspondingthreshold value, then in step 340 it is determined whether thecurrently-addressed tissue sensor probe, i.e., probe(x), is designatedas a threshold probe or a critical structure probe. If probe(x) is acritical structure probe, then in step 350 an alarm indication ispresented to the user, and step 365 is performed wherein the generator20 is deactivated, which may help reduce possible damage to the criticalstructure corresponding to probe(x). If probe(x) is a threshold probe,then a status indication is presented to the user in step 345 (toindicate ablation progress status) and the method proceeds to step 335as described hereinabove. In an embodiment, an additional test may beperformed wherein it is determined whether all threshold probescurrently in use, and/or all threshold probes within a designated probegroup, have exceeded the corresponding threshold thereof, and, if so,continue with step 365 to deactivate generator 20.

It is to be understood that the steps of the method provided herein maybe performed in combination and/or in a different order than presentedherein without departing from the scope and spirit of the presentdisclosure.

The described embodiments of the present disclosure are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present disclosure. Further variations of theabove-disclosed embodiments and other features and functions, oralternatives thereof, may be made or desirably combined into many otherdifferent systems or applications without departing from the spirit orscope of the disclosure as set forth in the following claims bothliterally and in equivalents recognized in law. The claims can encompassembodiments in hardware, software, firmware, microcode, or a combinationthereof.

1. An ablation system, comprising: a generator adapted to selectivelyprovide ablative energy; an ablation probe operably coupled to thegenerator and adapted to receive ablative energy from the generator andto deliver ablative energy to tissue; a controller operatively coupledto the generator, the controller including: a processor; a memoryoperatively coupled to the processor; a user interface operativelycoupled to the processor; a sensor interface circuit operatively coupledto the processor and adapted to receive at least one impedance sensorsignal from at least one tissue sensor probe; the at least one tissuesensor probe operatively coupled to the controller, and including: ashaft having a proximal end and a distal end and adapted for insertioninto tissue; and a first electrode and a second electrode disposed on anouter surface of the shaft and adapted to operably couple to the sensorinterface circuit to sense tissue impedance.
 2. The ablation system inaccordance with claim 1, wherein the controller includes an indicatorthat activates when a sensed tissue impedance parameter exceeds apredetermined threshold.
 3. The ablation system in accordance with claim2, wherein the indicator is selected from the group consisting of avisual indicator, an audible indicator, and a haptic indicator.
 4. Theablation system in accordance with claim 1, wherein the controller isoperable to deactivate the generator when a sensed tissue impedanceparameter exceeds a predetermined threshold.
 5. The ablation system inaccordance with claim 1, wherein the at least one tissue sensor probeincludes an identifier.
 6. The ablation system in accordance with claim5, wherein the controller is configured to receive identification datafrom the identifier.
 7. The ablation system in accordance with claim 1,wherein at least one of the first and second electrodes is annular inshape and disposed coaxially about the shaft.
 8. The ablation system inaccordance with claim 1, further including an actuator operativelycoupled to the controller and configured to selectively activate thegenerator. 9.-20. (canceled)
 21. An ablation system, comprising: agenerator adapted to selectively provide energy; an ablation probeoperably coupled to the generator and adapted to deliver energy totissue; a plurality of tissue sensing probes, the plurality of tissuesensing probes including at least one threshold probe and at least onecritical structure probe; a controller configured to determine whether asensed tissue impedance parameter from each of the plurality of tissuesensing probes exceeds a predetermined tissue impedance parameterthreshold, wherein, for the at least one critical structure probes, thepredetermined tissue impedance parameter threshold is indicative of apre-denaturation state of tissue and, for the at least one thresholdprobes, the predetermined tissue impedance parameter threshold isindicative of denaturation of tissue.
 22. The ablation system inaccordance with claim 21, wherein the controller is configured toautomatically deactivate the generator in response to a determinationthat the sensed tissue impedance parameter from each of the plurality oftissue sensing probes exceeds the predetermined tissue impedanceparameter threshold.
 23. The ablation system in accordance with claim21, wherein the predetermined tissue impedance parameter thresholdindicative of a pre-denaturation state of tissue is an initial rise inimpedance.
 24. The ablation system in accordance with claim 21, whereinthe predetermined tissue impedance parameter threshold indicative ofdenaturation of tissue is a rate of change of impedance exceeding apredetermined rate.
 25. The ablation system in accordance with claim 21,further comprising an actuator operatively coupled to the controller andconfigured to selectively activate the generator.
 26. The ablationsystem in accordance with claim 21, wherein at least one of theplurality of tissue sensing probes includes an identifier.
 27. Theablation system in accordance with claim 26, wherein the controller isconfigured to receive identification data from the identifier.